Presently it is conventional to inspect a workpiece for flaws or defects contained therein by ultrasonic non-destructive testing methods. These methods employ an ultrasonic transducer such as a piezoelectric crystal which when energized by an electrical stimulus radiates a pulse of ultrasonic energy into a workpiece. If the familiar pulse echo search unit is used, the ultrasonic energy is reflected back from a defect within the workpiece to the crystal whereby the mechanical vibrations caused by the ultrasonic energy are translated back into electrical signals. In this method the time of arrival of the return signal indicates the presence and exact location of the defect within the workpiece. On the other hand, when the familiar "through" transmission system is used a separate transducer is aligned opposite the workpiece and attenuations due to the defects in the workpiece or changes in the time of arrival of the signal is indicative of some characteristics of the workpiece.
This invention is directed to a testing machine wherein an ultrasonic testing search unit is moved along a contoured surface of a structure being tested. The test instrument is provided with equipment to produce liquid coupling between the search units and the contour of the structure being followed and tested.
Certain workpieces include curved or sloped shapes which are sometimes difficult to maneuver a search unit across. A number of different type systems have been employed to ultrasonically test curved or sloped workpieces. One such device is described in U.S. Pat. No. 3,721,118 and copending application for United States Letters Patent, Ser. No. 766,688, filed Feb. 2, 1977, now U.S. Pat. No. 4,140,954, both assigned to Automation Industries, the assignee of this invention. Ultrasonic search units for such testing are coupled to the workpiece being tested by use of liquid couplants. The liquid is injected into the space between the face of the search unit and the contoured surface. In view of the liquid coupling, the search unit should be located very close to the contoured surface. As a result of this, testing with presently available equipment is slow because of these constraints. In order to make such testing economic, and, accordingly, widely used, it is necessary to create a machine and a control system which permits rapid and accurate testing.
In general, the principle on which ultrasonic testing is based is the projection of ultrasonic energy into the workpiece with consequent reflection or transmission depending upon the nature of the workpiece. Testing may be accomplished either by analyzing the reflected portion of the signal or by analyzing the portion that is transmitted through the workpiece. In reflection type of ultrasonic analysis, both the transmitter search unit and the receiver are on the same side of the workpiece. In the case of through transmission testing, the transmitter search unit is located on one side of the workpiece while the receiver is located on the other side.
Under such circumstances, it is also necessary to provide a machine which accurately positions the receiver search units in alignment with and facing the transmitter search unit, while the transmitter search unit follows the contour of the part being tested.